Background Type 2 diabetes mellitus (T2DM) is a condition characterized by insulin resistance and progressive failure of the insulin-secreting beta-cells. Based on studies in small cohorts of young patients (especially Pima Indian offspring), we know that individuals with childhood onset T2DM are at very high risk for diabetes-related morbidity and mortality, due to a longer life-time duration of diabetes, as well as possible increased rapidity of beta-cell failure. Based on the currently largest available interventional trial, the TODAY study (Treatment Options for Diabetes in Adolescents and Youth), we know that T2DM in youth is associated with more rapid beta cell failure than in adults and that standard medical treatment is prone to fail in most patients. Our primary study objective is to acquire data on the natural history of T2DM in youth. Measurements will include indices of beta-cell function, body composition, cardiovascular disease risk factors, gut hormones, and psychological well-being. These data will be compared to findings in non-diabetic volunteers who are lean or overweight/obese. The study will also allow us to collaborate with other investigators in order to investigate factors (e.g. body composition changes, effect of life-style changes (such as sleep)) that determine the progression to and outcome of type 2 diabetes.